Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans.

Randomized, double-blind, placebo-controlled trial in healthy overweight adults in Norway. Eligible participants were 18 to 65 years old with BMI 25 to 30, and the active intervention arms included 61 participants in the CLA-free fatty acid group and 60 in the CLA-triacylglycerol group, alongside 59 placebo participants. The trial was conducted at two medical centers and participants consumed an ad libitum diet.

Participants received oral conjugated linoleic acid for 12 months as 6 softgel capsules daily. The active regimens were CLA-free fatty acid, 4.5 g/day containing 3.6 g active CLA isomers, or CLA-triacylglycerol, 4.5 g/day containing 3.4 g active CLA isomers; the comparator was 4.5 g/day olive oil placebo.

Long-term CLA supplementation reduced body fat mass compared with placebo, with similar fat-loss effects for CLA-free fatty acid and CLA-triacylglycerol. From month 0 to 12, body fat mass changed by 0.2 kg with placebo, -1.7 kg with CLA-free fatty acid, and -2.4 kg with CLA-triacylglycerol; body fat mass was significantly lower in both CLA groups versus placebo at 12 months (P = 0.001). CLA-free fatty acid also increased lean body mass relative to placebo, with a 0.7 kg increase versus 0.0 kg and 1.8% greater lean body mass than placebo (P = 0.002), and lean body mass was significantly higher at 12 months (P = 0.05). Adverse events were reported with similar frequency across arms, and tolerability was comparable to placebo.

The trial was modest in size, with about 60 participants per active arm, and it was conducted in a single country, which may limit generalizability. Participants followed an ad libitum diet and physical activity was self-reported, so lifestyle factors could have influenced body composition outcomes. Diet records were completed by 81.7% of subjects, leaving some missing dietary data.